Because, by far, the majority of people who post are those who have had problems. The thing is, aside from some initial side effects for a small number of patients, far less than 10% of users have effects that require stopping their medications...and most stop without professional advice from their doctors.
The other 90+% of users are too busy enjoying healthy, happy lives to be spending much time on forums...especially those sites where people scare you half to death with tales of their heads spinning in circles while they spew green vomit like the Exorcist!!